Propellent powder process



Patented Dec. 28, 1943 PROPELLENT POWDER PROCESS Charles Earnest Silk. Alton. m, mi ito Western Cartridge Company, East Alton, 11L, a corporation of Delaware No Drawing. Application December 3. 1938, Serial No. 243.767

14 Claims.

This invention relates to propelient powder and more particularly to an improved process for surface treating propellent powder grains in order to modify the characteristics thereof.

The object oi'this invention is to provide a process for the surface treatment of powder grains by means of which the treating agent is uniformly distributed among the grains under treatment. the absorption oi treating agent by the grains may be made to occur as rapidly as desired. and the rate and extent of impregnation may be readily controlled.

In the course of the development of smokeless powders. a number of substances for improving the ballistic properties and/or storage characteristics have become known. These are generally substantially non-volatile compounds which are usually solvents for the smokeless powder base.

.Those agents which afiect the burning rate of the resistance to moisture absorption of powders may likewise be improved by the addition of an acc'elerator or deterrent, although substances are known which may be added to accomplish these results specifically. for example, diphenylamine for enhanced stability.

Such treating agents have been added to the smokeless powder base either during the manufacturing operation prior to the fabrication of the grains, as exemplified by the process dein British Patent No. 6,448 of 1892, or

they have been added to the fabricated grains by a process of surface-treatment, for example, as

taught in United States Patents No. 1,862,914 and In accordance with the process as described in the above mentioned United States Patent No. 1,955,927. surface treatment of powder grains may be accomplished by means of an emulsion or dispersion of a combustion modifier in water, or by means of an emulsion or dispersion of a combustion modifier solution in water. In the latter instance the combustion modifier was extended with a volatile solvent for the same which was .cases there existed a tendency toward coalescence of the line globules of combustion modifier, or combustion modifier solution. to produce larger globules than were desirable, with the result that the application oi the treating agent was not uniform throughout the mass of grains being treated,

and, in the case of large grains. was not uniform over the suriace oi the individual grains. While this tendency toward coalescence could be overcome by stabilizing the dispersion or emulsion as by use of a protective colloid, the presence of the protective colloid appeared to further increase the resistance toward absorption.

A more specific object of the present invention is to provide a process oi suriace treating pro pellent powder grains wherein absorption of the treating agent is facilitated and the tendency of protective colloids and/or volatile non-solvents for the powder grains to inhibit absorption, overcome.

Other objects will become apparent to those skilled in the art when the following description is read:

In accordance with the present invention absorption of surface treating -agents by propellent powder grains is facilitated and accelerated. and in cases where the surface treatment is carried out in the presence oi a protective colloid, or in the presence of a volatile solvent for the treating agent which is not a solvent for the powder grains. the tendency of those materials to inhibit a so ption is overcome by the use of a relatively small quantity of volatile solvent which itself is a solvent for nitrocellulose. More specifically one phase oi the present invention contemplates the application of treating agents to smokeless powder grains according to a procedure in which the treating agent is applied to the grains in the form of a dispersion or emulsion of a composite volatile solvent solution. In such case one component of the solvent is a water immiscible nonsolvent for the smokeless powder base, while another component is a solvent for the smokeless powder base. During the treatment, the powder grains are advantageously maintained in suspension in the treating bath as by vigorous agitation. Uniform distribution oi the treating agent among the powder grains and over the surfaces oi the individual grains is thus insured by the dilution or extension of the treating agent with a solvent and by maintaining such solution dispersed in the tom of fine globules throughout he re ns bath by adequate agitation. The use oi a protective colloid may irequently be desirable to decrease the tendency toward coalescence or the dispersed globules of treating agent ture oi two or more such substances. Suitable accelerators are nitroglycerin, nitroglycol, and

other nitric acid esters oi polyhydric alcohols while nitrohydrocarbons such as dinitrotoluene.

non-volatile esters such as al yl phthalates, substituted ureas such as dimethyl-diphenyl-urea, and compounds at similar properties are suitable deterrents. The quantity of treating agent to be added to the powder base usually amounts to less than ten per cent by weight of the finished product. although the quantity at an accelerator such as nitroglycerin may be as high as fifty percent.

In accordance with this invention where the treating agent is extended by solvent which is a non-solvent for .the smokeless powder base. the treating agent is dissolved in a composite volatile solvent, one component of which is immiscible with water and is a non-solvent ior the smokeless powder base. while another component is a solvent for the powder base. The volatility oi the solvent mixture should be sufficiently high to permit the ready removal of the solvent from the grains following the surface-treatment and in general those with boiling points below about 150 C. have been found useiul. As illustrating some of the suitable water-immiscible non-solvents may be mentioned aromatic hydrocarbons such as benzene or toluene. chlorinated hydrocarbons such as ethylene chloride or trlchloroethylene, solvent naphthas, others such as isopropyi ether or normal butyl ether, and water-immiscible alcohols such as butyl or isobutyl alcohol. The quantity of such solvent that may be used with advantage depends on the quantity of treating agent it is desired to add to the grains, and may range from a weight equal to that of the treating agent when the latter amounts to tilt? percent the finished product to about ten to twenty times the weight of treating agent when one percent of the latter is being added. I

To complete the formation of the treating agent solution. there is added a volatile solvent for the smokeless powder base such as ethyl or isopropyl acetate. acetone; ethyl methyl or methyl isobutyl ketone. or ethylene glycol diethylether in the-case oi pyrocollodion type. of nitrocellulose. in an amount equal to 1596 to 100% of the amount of the above described non-solvent which is used. The quantity of solvent for the powder base may be varied according to the particular solvent used. the desired rate oi absorption. and the desired extent of penetration of the modiiler in the powder grains. Both the rate of abeorption and the extent of penetration are increased with increasing proportion of such solvent in the mixture. An excao of such solvent should Benerally be avoided since a tendency toward sticking and agglomeration of grains is caused thereby. while a quantity substantially less than the stated minimum has no appreciable eiiect.

The solution of treating agent in the composite solvent may be emulsified by means oi-suitable agitation in water containing suincient protective colloid to maintain the resulting fine droplets of solution in dispersed form until absorbed during the surface treatment of the powder grains. The treatment is preferably carried out by suspending powder grains in water by vigorous agitation and adding the solution of combustion modifier, or a preformed emulsion of combustion modifier solution. to the bath as agitation is continued. The treatment may be carried out at ordinary room or higher temperatures as desired. absorption of the droplets of treating agent solution being more rapid the higher the temperature. A temperature of 50 to C. has been found'to give good results. v

As an illustrative embodiment of this invention. nitrocellulose powder grains in the form of spherical droplets 0.010 inch in diameter, resulting from the process described in U. 8. Patent No. 2,027,114 to Olsen. Tibbitts, and Kerone, is sued January 6, 1936, may be surface treated as iollows:

300 pounds oi powder grains are suspended by thorough agitation in 1200 pounds of water contained in a suitable jacketed vessel and hot water or steam is applied to the Jacket so that the temperature of the powder-water suspension is raised to 65 C. To this suspension there is rapidly added an emulsion consisting oi a solu-- tion of 5: pound of gum arable in pounds of water in which there has previously been dis persed. by means of vigorous agitation. fine globnice of a solution containing 83 pounds of nitroglycerine, 33 pounds of toluene. 3.5 pounds of dinitrotoluene and 16 pounds of ethyl acetate. The dispersed globules of solution are thus uniformly distributed among the powder grains and their composition is such that they are completely taken up by the powder grains within iliteen minutes after the addition. In the absence of ethyl acetate or other nitrocelluloee sol-- vent which is.highly fluid. similarly dispersed droplets of solution remain unabsorbed by the powder grains even after sixty minutes agitation under the same conditions. when the desired extent of impregnation has been attained. as by continuing the agitation at 65 C. for thirty to sixty minutes. the suspension is cooled by passing cold water through the jacket. Less penetration oi the treating agent into the grains may be secured by decreasing the quantity oi nitrocellulose solvent. ethyl acetate in the present example. which is used. Aiter being cooled. the powder grains are ireed of excess water as by centrifuging. after which they are washed with cold water. and dried by means or air at 50' C. Finishing treatments, such as glazing with graphite, may then be applied according to lmown methods.

The stabilized aqueous emulsion oi the solution of treating agent may be prepared with the use of one or more of the known suitable emuisifyiile agents as, for example. water-soluble gums such as gum arable and gum tragacanth. dextrln. starch. water-soluble cellulose ether: such as methyl cellulose containing 22-28% methoxyi. casein. bentonite; alkali salts of sulfated higher alcohols. and the like. For best results, the quantity of emulsifying agent is adjusted so that separation into the component phases will occur in about 15 to 30 minutes after agitation has stoppedr Ii desired. a portion of the emulsifying scent may be added to the suspension oi powder grains prior to the addition oi the emulsion oi the modiiler solution.

Another example oi a process embodying the principles oi this invention comprise: the macetreatment oi powder grains prepared by ag omeration of fineIy-dlvided particles oi gelatinized nitrocellulose into clusters, which may range irom stitutea ior nitrocellulose such as nitroctarch or other nitrated carbohydrates, is likewise included within the scope oi this invention.

While in the ioresoing description oi the various embodiments oi the invention. the vehicle in a which the powder grains are suspended and in which the treating agent. or treating agent solutionisdispersedoremulslfledhasbeendeslgnated as water, it is to be understood that the invention 0.006 'to 0.018 inch in average diameter. as deisnct limited to the use oi water as the treating scribed in the copending application oi Olsen. Tibhitts and Korean, Serial No. @0332. filed June 30, 1932. The treatment is carried out in accordance with the procedure of the first example bath. on the contrary. it will be understood that any liquid vehicle which is not a solvent ior the treating agent, and consequently a vehicle in which the treating agent, or-treating agent soluabove, except that the added emulsion consists of tion. may be dispersed or emulsified in the term finely di persed globules oi a solution containing 32 pounds oi nitroglycerin, 32 pounds oi toluene, 1'1 pounds oi dibutyl phthalate. and 6 pounds oi ethyl acetate in 120 pounds oi water containing 55 ct globules, may be employed in lieu oi water; provided. oi course. that the chosen vehicle is not itself a solvent ior the smokeless powder base. Consequently in interpreting the ioregoing depound oi gum arabic. The reduction in the scription andinconstruing thenppended claims.

amount oi ethyl acetate as compared with the first example is made in view oi the presence in the solution oi the phthalate. which is a good solvent ior nitrocellulose.

In a third specific embodiment oi this invention, 300 pounds oi nitrocellulose powder grains as in the previous example may be suspended in 1,200 pounds oi water at 15'-30 C. while this suspension is vigorously agitated, there is added a solution containing '17 pounds of nitroglycerin.

17 pounds of benzene, 7.7 pounds oi dinitrotoluone. and pounds of acetone. Aiter 30 minutes agitation, the temperature oi the suspension is raised to 65 0., for example, by means of a suitable heating jacket. complet aiter 90 minutes agitation at 65 C. The acetone whichis used in this treatment not only cuts down the time ior eomplet absorption oi the globules 0i modifier solution by the powder grains The coating treatment is 5 the term "water" is intended as comprehensive oi such other vehicles.

It will be understood, therefore, that the present invention is not limited to the specific details oi the ioregoing description, but on the contrary, that various modifications in the procedure and changes in the proportion oi the ingredients and other details may be made by those skilled in the are without departing irom the spirit of this invention. It is to be distinctly understood, thereiore, that such modifications and the use oi such individual features and combination oi features as do not depart from the spirit at this invention are. although not specifically described herein,

from ninety minutes at 65 C. to thirty minutes, to W the P s comprising. treating smokeency to inhibit absorption of the treating agent by the powder grains the addition oi a small quantity, as ior example, ten to fiity per cent on the weight oi the treating agent, oi a solvent which itseli is a solvent ior nitrocellulose may be incorporated with the treating agent with the resuit that absorption of the treating agent is accelerated. In such cases where no solvent which is not a solvent for nitrocellulose is employed, the solvent for nitrocellulose may advantageously be of the type which is not substantially miscible with water.

The process oi this invention may advantageously be utilized ior the application, by sur- 'iace-'-treatment, oi treating agents to any wpe. size or shape of smokeless powder base grains. Grains of partly or completly gelatlnized nitrocellulose oi any desired state oi nitration which have been iabricated by any suitable process may be treated in accordance with this process and less powder grains in a non-solvent bath with a dispersion oi a solution, immiscible with the bath, composed of non-volatile combustion modifier. in a composite volatile solvent containing a solvent ior the powder grains and a non-solvent ior the J component oi the solution being immiscibm with the non-solvent oi the bath and continuing the treatment until the treating agent is deposited upon the grains.

3. In the art oi manuiacturlng propellent powder, the process comprising, treating smokeless powder grains with an aqueous dispersion oi a water immiscible solution of combustion modifier in a composite volatile solvent containin a solvent ior the powder grains and a non-solvent ior the same.

converted to a smokeless propellent powder havmg improved stability, resistance to moisture. enhanced progresslvity of combustion, and/or higher potential. The surface-treatment oi doublebase powder grains, containing nitrocellulose and nitroglycerin, as well as 01 grains containing sub- 4. In the art oi manuiacturing propellent p w der. the process comprising, treating smokeless powder-grains with an aqueous dispersion oi a water immiscible solution oi deterrent and accelerator in a composite volatile solvent containing a solvent ior the powder grains and a non-solvent ior the same.

5. In the art oi manufacturing propellent powders, the process comprising heating nitrocellulose grains with a stabilised emsemulsion oi a solution of a non-volatile treating agent in a composite volatile solvent containing a solvent for nitrocellulose and a non-solventfor the same. which is immiscible with water and continuing the treatment until the treating agent is deposited upon the grains.

6. In the art of manufactiu'ing propellant powders, the process comprising suspending smokeless powder grains in water, and adding to the suspension is stabilized emulsion of a solution of a non-volatile combustion modifier in a composite volatile solvent containing a solvent for nitrocellulose and a non-solvent for the same, which is immiscible with water and heating the mixture.

7. In the art of manufacturing propellent powders. the process of surface treating comprising, agitating smokeless powder grains in water containing dispersed globules 0! a non-volatile combustion modiiler dissolved in a composite volatile solvent composed of a solvent for the powder grains and a water-immiscible non-solvent for the same, in the presence of a protective colloid and continuing the agitation until the treating agent is deposited upon the grains.

8. In the art of manufacturing propelient powders, the process or surface-treating smokeless powder grains comprising, dissolving a nonvolatile combustion modifier in a mixed volatile solvent composed of a solvent and 0! a nonsolvent for the powder grains to term a water immiscible solution. emuisiiying the said solution in water containing an emulsifying agent, adding the said emulsion to an aqueous suspension of the powder grains and driving on the volatile solvent.

9. In the art of manufacturing propeilent powders, the process comprising, treating nitrocellulose grains with an emulsion 01 a solution of nitroglycerin in a volatile mixed solvent comprised of a solvent and a non-solvent for nitrocellulose, said solution being immiscible with the other phase of the emulsion and said other phase being a non-solvent for nitrocellulose the said emulsion being stabilized by means of a protective colloid.

10. In the art oi manufacturing propellent powders. the process comprising preparing a solution of nitroglycerin; toluene and ethyl acetate. emulsifying the said solution in water containing a protective colloid, and treating nitrocellulose rains therewith in aqueous s ll. In the art oi manufacturing propelient powder the process comprising. preparing a solution of nitroglycerin, benzene, and acetone, emulsifying the said solution in we and treating nitrocellulose grains therewith in aqueous suspension.

12. In the art of manufacturing propellent powder the process comprising. preparing a solution of nitroglycerin in a solvent mixture containing a component, which is a solvent for nitroglycerin but a non-solvent for nitrocellulose, and which is immiscible in water, and another component which is a solvent for both nitroglycerin and nitrocellulose, emulsifying the said solution in water containing a protective colloid, and treating nitrocellulose grains therewith in aqueous suspension.

18. In the process of surface treating smokeless powder grains wherein the powder grains are suspended in a water bath containing a stabilized emulsion of non-volatile liquid combustion modiiler, the step of overcoming the tendency of the stabilized emulsion to inhibit absorption of the combustion modifier by the powder grains which comprises, adding a small quantity of a volatile liquid which is a solvent for both the powder grains and the combustion modifier.

14. In the process of surface treating smokeless powder gralns wherein the powder grains are suspended in a water bath containing a stabilized emulsion of non-volatile liquid combustion modiiler, the step of overcoming the tendency of the stabilized emulsion to inhibit absorption of the combustion modifier by the powder grains which comprises, adding a small quantity of a volatile liquid which is a solvent for boththe powder grains and the combustion modifier, said volatile liquid bein immiscible with the water phase of the emulson.

CHARLES EARNEST SILK. 

